Two stage heat treatment of cobalt molybdate catalysts



United States Patent 3,415,760 TWO STAGE HEAT TREATMENT OF COBALTMOLYBDATE CATALYSTS David James Hadley, Epsom Downs, Surrey, and RowlandHarris Jenkins, West Ewell, Surrey, England, assignors to The DistillersCompany Limited, Edinburgh, Scotland, a British company No Drawing.Continuation of application Ser. No.

337,999, Jan. 16, 1964, which is a division of application Ser. No.134,592, Aug. 29, 1961. This application June 28, 1967, Ser. No. 649,743Claims priority, application Great Britain, Sept. 8, 1960, 30,923/ 60;Sept. 29, 1960, 33,411/60 6 Claims. (Cl. 252-470) ABSTRACT OF THEDISCLOSURE Process for preparing an oxidation catalyst containingcobalt, molybdenum and oxygen in which the atomic ratio of cobalt tomolybdenum is not substantially greater than 1:1, by adding anitrogenous base to a solution of a cobalt salt and molybdic acid ormolybdates of a nitrogenoils base to obtain a solution of pH less thanabout 7, forming a precipitate in said solution, heating theprecipitate-,to 350 to 650 C., pelleting the material preferably aftergrinding, and then subjecting the pelleted material to a second heattreatment in the range of 500 to 650 C.

This application is a continuation of application Ser. No. 337,999 filedJan. 16, 1964, now abandoned, which is a division of application Ser.No. 134,592 filed Aug. 29, 1961, now abandoned.

The present invention relates to the production of unsaturated aliphaticacids such as acrylic acid and methacrylic acid.

According to the present invention the process for the production ofacrylic acid or methacrylic acid comprises reacting at an elevatedtemperature in the vapour phase acrolein or methacrolein with molecularoxygen over an oxidation catalyst comprising an oxide compositioncontaining cobalt, molybdenum and oxygen in which the atomic ratio ofcobalt to molybdenum is not substantially greater than 1:1 prepared byadding a nitrogenous base to a solution of a cobalt salt with molybdicacid or a molybdate of a nitrogenous base to obtain a solution of pHless than about 7, forming a precipitate in said solution, heating thesaid precipitate at about 350 to 650 C., subjecting the resultingmaterial to frictional forces and heating it at about 500 to 650 C.

The catalytic oxide composition containing cobalt, molybdenum and oxygenof the present invention is suitably formed by mixing an aqueoussolution of a cationic cobalt salt, such as the nitrate, chloride, oracetate, with an aqueous solution or suspension of molybdic acid or amolybdate, adding a nitrogenous base to the aqueous mixture in aproportion for example between about 0.5 and about 1.5gramme-equivalents of base per gramme-atom of cobalt such that the pH ofthe mixture does not exceed about 7, filtering off and drying theresulting precipitate, and subjecting this to the double heat treatmentaccording to the invention. Besides ammonia a wide variety ofnitrogenous bases can be used, such as the aliphatic amines, forinstance ethylamine and triethylamine, ethanolamine ethylene diamine,aromatic or heterocyclic amines such as aniline and pyridine, andcycloaliphatic amines, such as piperidine. The preferred nitrogenousbase is ammonia. The temperature at which the precipitation is carriedout is not critical, and temperatures between room temperature and about100 C. are suitable. It is preferred to carry out the precipitation attemperatures above room 3,415,760 Patented Dec. 10, 1968 temperature, asthe precipitate produced at these temperatures is more easily filtered.

After being dried, for instance at about 100 C., the composition issubjected to a first heat-treatment at about 350-650 C., after which thematerial is subjected to frictional forces, for instance by being formedinto pellets preferably after first being ground. The catalyst is thensubjected to a second heat-treatment at about 500 to 650 C. preferablyat about 600 C. It is found that by use of this preferred two-stageheat-treatment a harder catalyst is obtained and that the granules ofcatalyst have less tendency to break up through attrition.

The precipitated catalyst composition, which is blue in colour, (Blue I)after being dried, is subjected to the first heat-treatment in which itundergoes a phase change to produce a material also blue in colour (BlueII), but

whichgives a different X-ray diffraction pattern. On subjecting thismaterial to frictional forces, eg by grinding or pelleting, a furtherphase change together with a change in colour to green or blackdepending on the state of subdivision of the particles, is obtained.Heating this ground material produces a reversal of phase change to givethe material Blue 11 produced after the first heat-treatment. Thissecond heat-treated material however possesses substantially increasedresistance to wear, i.e. when the Blue II phase is approached from thegreen or black phase the pellets are harder than if the approach is fromBlue I to Blue II} The atomic ratio of cobalt to molybdenum in thecatalyst may vary within moderately wide limits, for instance from 0.5:1 to 1:1 but should not be substantially greater than 1: 1.

The catalyst composition of the present invention is particularly usefulin the process for the production of acrylic or methacrylic acid by thevapour phase reaction of acrolein or methacrolein, or compounds yieldingthese substances under reaction conditions, e.g. propylene or isobutene,with molecular oxygen.

The reaction may be carried out in any suitable manner, for instanceunder isothermal or adiabatic conditions and as a fixed or fluidised bedprocess. The proportion of aldehyde in the feed may vary within widelimits, for example between 1 and 20% by volume, and preferably betweenabout 2 and 10% by volume. The concentration of oxygen in the feed mayvary within moderately wide limits, for example between 1 and 20% byvolume and preferably 2 and 15% by volume. The molecular oxygencontaining gas may be supplied as air.

The reaction is suitably carried out in the presence, as diluent, of agas which is substantially inert under the conditions of reaction, forexample, nitrogen, propane, butane, isobutane, carbon dioxide and steam.It is preferred to use steam or nitrogen or mixtures thereof. Theconcentration of the steam may vary within wide limits, for instancebetween 20 and 60% by volume of the feed.

The reaction is carried out at an elevated temperature, for instancebetween 250 and 600 C. and preferably between 300 and 500 C.

The contact time may be for example in the range 130 seconds.

The process of the present invention is further illustrated by thefollowing examples. In the examples, parts by weight and parts by volumebear the same relation to each other as to kilograms to litres.

Example 1 14 5.5 parts by weight of cobalt nitrate was dissolved in 60,parts by weight of water at 60 C., and 88.3 parts by Weight of ammoniummolybdate, powdered to 30 mesh B.S.S. was dissolved in 260 parts byweight of water at 60 C. The two solutions were mixed and maintained at60 C. with stirring, while 68.4 parts by weight of triethylamine wasadded over a period of 30 minutes; stirring was continued for a further15 minutes. The resultant mixture gave a pH of 5.2 with a glasselectrode under the conditions specified above. The precipitate wascollected and washed twice by resuspension in 333 parts by weight ofwater. The washed precipitate was dried at 110 sieved through 8 meshB.S.S. and heat treated at 600 C. for 16 hours. The heat treatedmaterial was then ground to 30 mesh B.S.S. pelleted and subjected to asecond heat treatment at 600 for 16 hours.

A gaseous mixture of 10.1% by volume of acrolein, 48.6% by volume ofnitrogen, 9.9% by volume of oxygen and 31.4% by volume of steam waspassed over the catalyst in a reactor at 397 the contact time being 3.5seconds.

Of the acrolein fed to the reactor 60.0% was converted to acrylic acid;9.2% was recovered unchanged. The yield of acrylic acid based on theacrolein consumed was 66.1%.

The hardness of the catalyst, measured by an attrition test in a rodmill under standard conditions was 93%. A second catalyst was preparedin a similar manner, but given only a single heat treatment; whereas theperformance of the catalyst in converting acrolein to acrylic acid wassimilar to the twice-heated catalyst, the hardness was only 66% measuredby the same test.

Example 2 582 parts by weight of cobalt nitrate was dissolved in 240parts by weight of water, and the solution was heated to 60 C. 353.2parts by weight of ammonium molybdate was dissolved in 1040 parts byweight of distilled water at 60 C.; the two solutions were mixed andwell stirred. 380 parts by volume of ethanol-amine (5.0 N aqueoussolution) was added dropwise over 30 minutes and the temperature of themixture kept at 55 60 C. The mixture was stirred for a further 15minutes after the addition was completed. The resutlant mixture gave apH of 6.0 with a glass electrode under the conditions specified above.The precipitate was filtered 01f, washed twice by resuspension with 1500parts of water, and dried in an oven at 110 C. The resulting granuleswere ground to 8 mesh B.S.S. and heated at 400 C. for 16 hours. The heattreated material was ground to 30 mesh B.S.S. pelleted and the pelletsgiven a second heat treatment at 600 C. for 16 hours.

A gaseous mixture of by volume of acrolein, 10% by volume of oxygen, 50%by volume of nitrogen, and 30% by volume of steam was passed over thecatalyst maintained in a reactor at 360 C. the contact time being 3.5seconds.

or the acrolein fed to the reactor 59.5% was converted to acrylic acid,and 13.7% was recovered unchanged. The yield of acrylic acid based onacrolein consumed was 69.0%.

As a comparison a record catalyst was prepared as described above exceptthat 600 parts of ethanolamine were employed leading to a pH of thefinal mixture of 7.9. After drying and heat treating, the catalyst wasfound to be almost completely inactive giving only a 3% yield of acrylicacid based on the acrolein fed at 380 C.

Example 3 291 parts by weight of cobalt nitrate was dissolved in 120parts by weight of distilled water, and the solution was heated to 60C.; 176.5 parts by weight of ammonium molybdate was dissolved in 520parts by weight of distilled water at 60 C. The two solutions were mixedand well stirred.

397 parts by volume of diethylamine (2.52 N aqueous solution) was addeddropwise over a period of 30 minutes and the temperature of the mixturekept at 5560 C. The mixture was stirred for a further minutes after theaddition was completed. The precipitate was filtered off, washed twiceby resuspension with 1000 parts by weight of distilled water, and driedat C. The resulting granules were ground to 8 mesh B.S.S. and heated at600 C. for 16 hours. The granules were then ground to 30 mesh B.S.S.pelleted, and the pellets subjected to a second heat treatment at 600 C.for 16 hours.

A gaseous mixture of 10% by volume of acrolein, 10% by volume of oxygen,50% by volume of nitrogen, and 30% by volume of steam was passed overthe catalyst maintained in a reactor at 380 C., the contact time being3.6 seconds.

Of the acrolein fed to the reatcor 63.4% was converted to acrylic acid,and 11.0% was recovered unchanged. The yield of acrylic acid based inacrolein consumed was 71.2%.

Example 4 291 parts by weight of cobalt nitrate was dissolved in partsby weight of distilled water, and the solution heated to 60 C. 176.5parts by weight of ammonium molybdate was dissolved in 520 parts byweight of distilled water at 60 C. the two solutions were mixed and wellstirred. 217 parts by volume of piperidi-ne (4.61 N aqueous solution)was added dropwise over 30 minutes and the temperature of the mixturekept between 55 to 60 C. The mixture was stirred for a further 15minutes, after the addition was completed. The resultant mixture gave apH of 5.3 with a glass electrode under the conditions specified above.The precipitate was filtered off, washed twice by resuspension with 1000parts of distilled water and dried at 110 C. The resulting granules wereground to 8 mesh and heated at 600 C. for 16 hours. The heat treatedmaterial was ground to 30 mesh B.S.S. pelleted and the pellets heated at600 C. for 16 hours.

A gaseous mixture of 10% by volume of acrolein, 10% by volume of oxygen,50% by volume of nitrogen, and 30% by volume of steam was passed overthe catalyst maintained in a reactor at 360 C., the contact time being3.6 seconds.

Of the acrolein fed to the reatcor 61.7% was converted to acrylic acid,and 8.9% was recovered unchanged. The yield of acrylic acid based onacrolein consumed was 67.8%.

Example 5 Ammonium molybdate, 353.2 parts by weight, was ground to lessthan 30 mesh B.S.S. dissolved in 1040 parts by volume of distilled waterat 60 C. and added to a solution of 582 parts by weight of cobaltnitrate dissolved in 240 parts by volume of distilled water at 60 C. Thewell stirred mixture was maintained at 60 C. whilst 420 parts by volumeof a 4.77 N aqueous 1:2-diamino-ethane (ethylene diamine) solution wasadded dropwise over 30 minutes. The resultant mixture gave a pH of 4.8with a glass electrode under the conditions specified above. Thereaction mixture was then stirred for a further 15 minutes, theprecipitate of cobalt molybdate filtered oft, washed twice byresuspension in 1500 parts by volume of distilled water each time, andfinally dried in air at 110 C. for 16 hours. The dried catalyst (453.4parts by weight) was ground and sieved to less than 3 mesh B.S.S. andheated in granular form in air at 600 C. for 16 hours. The heatedcatalyst was then ground and sieved to less than 30 mesh B.S.S. and thepowder formed into 3 mm. diameter pellets with the addition of 2% W./W.of graphite. Finally, the pelleted catalyst was heated at 600 for 16hours in air.

A gaseous mixture consisting of acrolein, 10.5% by volume, oxygen 9.2%by volume, nitrogen 52% by volume and water vapour 27.7% by volume waspassed over the catalyst described above at a reaction temperature of378 C., the contact time being 3.46 seconds.

Of the acrolein fed 62.5% was converted to acrylic acid and 11.9% wasrecovered unchanged. The yield of acrylic acid based on acroleinconsumed was 71.0%.

Example 6 A catalyst was prepared in an identical manner to the catalystdescribed in Example 5, except that 512 parts by volume of a 4.69 Naqueous ethylamine solution was used in place of the 420 parts by volumeof a 4.77 N aqueous 1:2-diaminoethane (ethylene diamine) solution, theresultant mixture having a pH of 5.9 with a glass electrode under thespecified conditions.

A gaseous mixture consisting of acrolein 9.7% by volume, oxygen 9.8% byvolume, nitrogen 50.3% by volume and water vapour 30.2% by volume waspassed over the catalyst at a reaction temperature of 380 C. the contacttime being 3.58 seconds.

Of the acrolein fed 69.4% was converted to acrylic acid and 12.7% wasrecovered unchanged. The yield of acrylic acid based on acroleinconsumed was 79.5%.

Example 7 119 parts of cobaltous chloride were dissolved in 150 parts ofwater at 60 C. and 88.8 parts of ammonium molybdate dissolved in 100parts of water at 60 C.

The two solutions were mixed and 100 parts of a 5.14

N solution of ammonia representing 0.75 gramme-equivalents of ammoniaper gramme-atom of cobalt, was added during 30 minutes. The precipitatewas filtered and washed thoroughly with distilled water, dried at 80 C.and heated at 350 C. in air. The resulting powder was pelleted andheated at 540 C. for 16 hours. The catalyst, tested under the conditionsof Example 1, gave a yield of acrylic acid, based on the acroleinconsumed, of 67.5%. Of the acrolein fed to the reactor 64.5% wasconverted to acrylic acid.

Example 8 A catalyst was prepared as in Example 7 except that cobaltacetate (125 parts) was used in place of the cobalt chloride. After heattreatment at 540 C. for 16 hours, this catalyst gave on test under theconditions of Example 1, a yield of acrylic acid, based on the acroleinconsumed, of 72%. Of the acrolein fed to the reactor 60.7% was convertedto acrylic acid.

Example 9 This example illustrates the improved hardness of catalystssubjected to the two-stage heat treatment in accordance with theinvention.

145.5 parts by weight of cobalt nitrate (CO(NO 6H O and 88.8 parts byweight of ammonium molybdate (NHQ MO O -4H O were dissolved in 320 partsby weight of water at 60 C., 108 parts by weight of 'a 5.14 N aqueoussolution of ammonia, representing 1.15 gramme-equivalents of ammonia pergramme-atom of co 'balt, was slowly added over a period of half an hour,and the mixture was stirred for a further minutes. The resultant mixturegave a pH of 5 with a glass electrode under the conditions specifiedabove. The precipitate was filtered off and washed twice by resuspensionwith 500 parts of distilled water. The precipitate was dried at 110 C.,and the powder was subjected to a heat treatment at 400 C. for 16 hours,then pelleted and the pellets heated at 600 C. for 16 hours.

A second catalyst was made up under identical conditions except that itwas subjected to a. single heat treatment at 600 C. for 16 hours.

The table below shows that the two catalysts had about the sameperformance, but that the twice heated catalyst was harder. The hardnessof the catalysts was compared by an attrition test in a rod mill understandard conditions.

TABLE 1 What is claimed is:

1. A process for the production of an oxidation catalyst comprising anoxide composition containing cobalt, molybdenum and oxygen in which theatomic ratio of cobalt to molybdenum is not substantially greater than1:1 which comprises adding ammonia or an aliphatic, aromatic orheterocyclic amine to a solution of a cobalt salt with a molybdenumcompound selected from the group consisting of molybdic acid andmolybdates of nitrogenous bases to obtain a solution of pH less thanabout 7, forming a precipitate in said solution, heating the saidprecipitate at about 350 to 650 C., forming said precipitate intopellets and heating said pellets to about 500 to 650 C., said heatingsteps being performed prior to use of said composition as a catalyst.

2. The process as claimed in claim 1 wherein the material subjected tothe heat treatment steps is prepared by mixing an aqueous solution of acationic cobalt salt with an aqueous solution of the molybdenumcompound, and adding ammonia or an aliphatic, aromatic or heterocyclicamine to the aqueous mixture to form a precipitate.

3. The process as claimed in claim 1 wherein ammonia is used.

4. The process as claimed in claim 1 wherein an aliphatic amine is used.

5. The process a claimed in claim 4 wherein the aliphatic amine isselected from the group consisting of ethanolamine, ethylamine,triethylamine or ethylene diamine.

6. The process as claimed in claim 1 wherein the precipitated materialis subjected to frictional forces prior to being pelleted.

References Cited UNITED STATES PATENTS 2,570,882 9/1951 Stiles 252-4723,087,964 4/1963 Koch et a1. 252-470 3,098,102 7/1963 Bethell et a1.252-470 DANIEL E. WYMAN, Primary Examiner. P. E. KONOPKA, AssistantExaminer.

US. Cl. X.R. 252-438; 260-530

